Fuel cell power plants which are used in space applications, such as in manned orbiters, unmanned satellites or the like will be exposed to ambient air surface conditions prior to, and during, launch, and upon re-entry, if any, and will also be exposed to space vacuum conditions when in orbit. When the fuel cell power plants are in operation, operation temperatures are sustained from the heat that they generate via the exothermic electrochemical reaction which occurs in the cells. In order to sustain operating temperatures at low operating powers and without necessity for inefficient electrical heaters, the power plant should be insulated against loss of heat. A problem arises in connection with the manner in which heat is lost from the power plant in the two different environments. In the vacuum environment of space heat is lost mainly by radiation, while in the ambient air environment heat is lost mainly by convection. The insulation used thus must be able to protect against each of these modes of heat loss. In addition, the insulation should be sufficiently flexible and yet durable so as to be able to be wrapped about the fuel cell power plant assembly, and conform closely to the surface contours thereof. This is required to eliminate formation of air paths between the insulation and the part that would permit either a forced airflow, or a "chimney" type air circulation resulting in a heat loss.